1. Field of Invention
Embodiments relate generally to apparatuses and methods for charging the batteries of a UPS. Specifically, at least one embodiment relates to charging UPS batteries in circumstances where the UPS has been supplied with additional external batteries to increase run time.
2. Discussion of Related Art
Uninterruptible power supplies (“UPS”) are used in a variety of applications to provide power to electrical loads, for example, loads that are intended to operate during interruptions in a primary source of electrical power. In general, a UPS includes, or is connected to, both a primary source of power and an alternate source of power where the alternate source of power can be employed to supply power to the electrical load when the primary source is not available. Often, the primary source of power is an AC power source such as power supplied from an electric utility. The alternate source of power generally includes one or more batteries supplying DC power.
The batteries are generally recharged after use by a battery charger coupled to the UPS. The standard battery capacity supplied with a UPS is generally selected to provide about 4 to 5 minutes of run time at the rated output power. However, in some instances a user may add extra batteries to extend the run time (i.e., the time for which the UPS is able to supply back up power to the load). The maximum charger rating for a UPS is typically about 10% of the rated output power. This charger rating is usually adequate to recharge the standard battery capacity supplied with the UPS in about 2-3 hours. However, this recharge time may become greatly extended if the user has added extra batteries. Depending on the extra battery capacity, the charging time, because of limited charger power, may become unacceptably long.
A common solution to this problem is to add an external battery charger to supplement the UPS internal battery charger and reduce the recharge time. The external charger is installed across the batteries. An important issue that must be addressed with this approach is matching of the performance characteristics of the UPS internal charger and the external charger. Furthermore, with the addition of the external charger, the UPS may lose its ability to detect faults and/or abnormalities with the battery system and may lose accuracy with respect to predicting run time.